1. Field of the Invention
The present invention relates to the field of monitoring and detection devices, and more particularly to a novel device for monitoring and detecting the speed and/or fan or blower failure when particularly used in connection with the cooling of electronic components in a computer.
2. Description of the Prior Art
In the past, it has been desirable to provide a monitoring means for automatically sensing, detecting or determining the speed of a fan or blower and/or to determine when the fan has failed, slowed down or even stopped. The result of such failure is to permit electronic components in the computer to heat and cause circuit failure. One prior attempt to monitor the operation of a cooling fan was to detect the fan's speed by sensing the rate at which an optical path was interrupted by the fan blades. Another attempt is represented by a device and circuit to monitor the fan speed by using a magnetic means to sense the rate at Which the magnetic field created by the fan motor is rotating. Still a further attempt relates to monitoring the cooling air flow by sensing air flow pressure such as with a microphone. Some of these prior attempts are more clearly disclosed in U.S. Pat. No. 3,885,200 and U.S. Pat. No. 4,479,115.
These prior approaches and circuits have created problems and difficulties since their size and complexity requires mounting in close proximity to the fan which is not always possible in compact devices such as in the manner that computers are manufactured at the present time. In some cases, it is not possible to mount prior monitoring devices since the fan mounts on heat sinks and particularly in instances where a microprocessor fan is employed. Also, monitoring the fan operation employing a thermistor requires that the device be mounted in front of the fan which is not always possible. Therefore, it can be seen that physical mounting problems for the prior devices are not easily solved and that such devices would be subject to dust and lint that would block instances where light paths are used for monitoring purposes.
Therefore, a long-standing need has existed to provide an electrical circuit which may be readily introduced into the connection between a computer power supply and the cooling fan for components thereof which need not require special mounting mechanisms and which will sense or monitor operation of the fan in a purely electrical way so that optics, sound pressure waves or the like are not relied upon in the detection portion of the circuit.